1. Engineering Research Center in Biomaterials Sichuan University Chengdu Sichuan 610065 P. R. China
2. Metrology Research Centre National Research Council Canada Ottawa Ontario K1A 0R6 Canada
3. Department of Ophthalmology West China School of Medicine West China Hospital, Sichuan University Chengdu Sichuan 610065 P. R. China
4. Institute of Atomic and Molecular Physics Sichuan University Chengdu Sichuan 610065 P. R. China